Furnace for roasting ores and such like operations



Feb. 13, 11923.

A. V. LEGGO FURNACE FOR ROASTING ORES.'AND SUCH LIKE OPERATIONS 6sheets-sheet 1 F1 1 ed May 18, 192 2 Feb. 13, 23.

' A. v. LEGGO YFURNACE FOR ROASTING ORES AND sum-{LIKE OPERA'HTORS FiledMay 18, 1922 6 ahebt5;1- ie% z Fella 13, 1923. 1,444Q927 A. v. LEGGOFURNACE FOR ROASTING ORES AND SUCH LIKE OPERATIONS Filed May 18, 1922 6sheets-sheet Feb. 13, 1923. 1,444,927

' A. v. LEGGO- FURNACE FOR ROASTING ORES AND SUCH LIKE OPERATIONS FiledMay 18;1922 6 sheetsshee 4 Feb 13, 1923. 1,444,927

A. V. LEGGO FURNACE FOR BOA STING ORES AND SUCH LIKE OPERATIONS FiledMay 18, 1922 6 sheets-sheet 5,

Feb. 13;, 1923; 1,444,927

A. V.- LEGGO FURNACE FOR ROASTING ORES AND SUCH LIKE OPERATIONS FiledMay 18, 1922 v 6 sheets-sheet 6 Patented Feb, 13, 192?.

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FURNACE ron noasrrus on-Es Application filed m 18,

To all wfiomitmay com/em: Be it known that An'riron VIc'ron LEGGO,subject of the King of Great Britain, residing at 4-97 Collins Street,li lelbourne, in the State of Victoria, Commonwealth of r-iustralia, hasinvented certain new and useful improvements in Furnaces tor RoastingGres and Such likeOpei-ations, of which the following is aspecification.

T his invention relates to an improved fur: nace for roasting ores andsuch like operations and rciters more especially to furnaces havingsuperimposed circular or approx imately circular hearths and adapted forroasting, suli'ihatinfg', dcyhdrating or such like operations.

Superimposed circular hearth furnaces having rotating rabbles havehitherto been constructed with one central column carry,- ing thesupporting arms for the rabble teeth which serve to move the ore undertreatment on one hearth from the centre to the periphery and vice versaon the next hearth and so on in a zig-zag manner radially through thefurnace, at the samejtime the rabbles serve to continuously expose:t'resh surfaces of the ore particles to the furnace gases.

' ln order to increase the size of the roasting units with this type'offurnace, it-has beenthe practice to increase the diameter and in somecases the number of the hearths but ithas been found that there is aneconomic limit beyond which this increase should not be carried.

For example, any increase in the diameter and capacity of the furnaceinvolves a corresponding increase in the size of the column and the sizeand length of the rabble arms. These increases require a considerableincrease in the height of each roasting chamber (especially whenprovision is made for circulation of a cooling medium through the rabblearms). Now it is recognized in metallurgical practice that is generallydesirable that the roasting chambers should be as low as possiljile-inorder to conserve heat and to ensurethat the ore particles come intointimate contact with. the furnace gases and this is especiallyimportant when the gases are to be utilized tor the manufacture oisulphuric arid and other industrial purposes.

FllltllEl'll'lOl'Q, when arms are used through which a cooling medium iscirculated, they have certain pronounced metallurigical and mechanicaldisadvantages; these are, that in AND soon LIKE ornnarrous.

1922. Serial No. 561,812. I

many operations it is undesirable to remove heat from some of the stagesof the roast (even if the heat so removed can be returned to the furnaceelsewhere) and the complex arrangements necessary to detachaloly fix theturns to the column-whilst at the same time maintaining the circulation,of the cooling medium; i

A d sadvantage incidental to the use of long 1' wieldiness is that therelatively high velocity of the outer end of the arms leads to an-uneven distribution of ore over the hearthsi The annular area whichcontains the ports on an outward ra-bbled hearth is comparatively bareunder operating conditions and therefore ineliicient; whilst withcertain ores (notably those containingv zinc or lead) any ore lei'tunstirred beneath the teeth will set into hard cakes if leit exposed tothe furnace gases. The removal of. these cakes involves an arduousoperation and inmany. "ases stoppage of the furnace. Anotherdisadvantageincidental to an in crease in the size and capacity ofcircular furnaces of this type is in connection with the circulation oigases for which large port must be prov1ded with consequent re ductionof active hearth area.

The object of the present invention is to provide an improvedconstruction of furna'ce'of the above mentioned type (that is'to sayhaving si'iperimposed circular or approximately circular hearths)whereby greatly increased size and capacity maybe secured in thefurnace. without incurring the 7 above mentioned disadvantages whilst atthe same time more eihcient roasting and such ;like operations maybeeffectedl v I accomplish, the above mentioned object by providing acircular (or approximately circular) furnace havinpysuperimposedheart-hs provided witha plurality of: vertical rabble sha'lts disposedsymmetricallyabout the centre of the said hearths and fitted with rabblearms of a length substantially than the radius of the said hearths andadapted tomovein overlapping paths whereby the material on the heartbswill be eflectuallv rabbled and moved progressively through the furnace.o i

The arrangement of the rabble shafts and arms is such that certainportions of the hearths formed on two sides by the orbits of the rabblesand on the otherside. by the inner face of the outer wall oi the furnacebble arms in addition to their un lOO are outside the area coveredby therabbles and are utilized to accommodate drop holes and (or) fines. Theseportions are hereinafter referred to for purposes of definition as cuspshaped spaces or cusps. This arrangement moreover enables a furnace tobe so constructed as to obviate many of the disadvantages above referredto and to be readily adapted to the mostexacting requirements of anyparticular kind or condi tion ormaterial to be treated.

Ar salient advantage of this arrangement is that it permits of the useof short rabble arms in a large diameter furnace which rabble arms canbe made of small. vertical section and in turn permits of the roastingchambers being built sufiiciently shallow to be most eliicientmetallurgically.

Moreover, such short arms when constructed ofspecial material do notrequire cooling and consequently the mechanical and metallurgicaldisadvantages incidental to the employment of cooled arms are obviated.

The symmetrical. arrangement of the rabble shafts fitted with short armsabout the centre of the furnace enables such cen tral portion ofthefurnace to be utilized for accommodating a stationary central columnadaptable. for the transference of air or gases from one portion toanother or for the purpose of preheating air for delivery to one or moreroasting chambers of the furnace, or for supplying cooling air whenrequired.

In order that the invention may be readily understood reference will nowbe had to the accompanying sheets of explanatory drawings wherein- IFigure 1 is a view in perspective of a furnace constructed in accordancewith the invention.

Figure 2 is a view in perspective of the lower part of the furnace andshows part of the internal construction thereof. The rabble arms areshown without teeth for convenience of illustration.

F igure 3 is a view in sectional elevation of the furnace portion beingshown broken away for convenience of illustration.

Figure 4 is a view in sectional. plan taken on the dotted line 4-4 ofFigure 3.

Figure 5 is a view in sectional plan taken on the dotted line 5-5 ofFigure Figure 6 is a view in sectional plan taken on'the dotted line 6-6of Figure 3.

Figures '7 and 8 are diagramn'iatic views of two succeeding l'learths ofa furnace and show another method of arranging the ore and gas ports toobtain a different circulation of the ore and gases through the .fur-

nace.

Figure 9 is a diagrammatic view of a- Figure 11 is a View similar toFigure showing five rabble shafts in the furnace.

Figure 12 is a view similar to Figure 10 showing six rabble shafts inthe furnace, the alternate shafts carrying shorter arms than thoseoperating on both sides thereof.

Figure 18 is a diagrammatic view of an inward rabbled hearth of afurnace having a plurality of rabbles placed symmetrically around acentral rabble shaft.

Figure 14: is a view similar to Figure 13 showing an outward rabbledhearth.

Figures 15 and 16 are diagrammatic views of two succeeding hearths of afurnace in plan, showing a further arrangement of the ore and gas portswhereby a third method of circulating the ore and gases is obtained.

Figure 17 is a view in sectional elevation of partof a furnace having acentrally disposed air circulating column.

Figure 18 is a diagrammatic view representing a sectional plan of Figure17 taken on the dotted line 18-l8. I v

' Figure 19 is a View in sectional elevation of a furnace having acentral air circulating column provided with radiating muflies.

Figure 20 is a view in sectional plan of I part 0f Figure '19 taken onthe dotted line 2020 portions being shown broken away for convenience ofillustration.

Figure 21 is aview in sectional plan of the furnace showing a modifiedform of mufile. Figure 22 is a View in sectional elevation of part of afurnaceprovided with muflies constructed as shown in Figure 21.

'In these drawings the numeral desig nates the furnace casing or shell.which preferably is made circular in form and has a series ofSUPGIiD'IPOSGCl hearths 31 over which the material under treatment ismoved by mechanically operated rabbles adapted to stir the material soas to continuously expose all particles of it to the action of the gasesin the furnace.

The rahbling mechanism comprises a plurality of rabble shafts 32 whichpass through all the hearths and are symmetrically arranged around thecentre of the furnace and provided with short rabble arms 33 of ap )i(')\"8 .l construction. I

' It will. be obvious from the following deucrig'ition of diifcrentarrangements of rah-- ble shafts that to obtain the advantagesincidental to a furnace constructed in accordance with this invention atleast three rabble shafts must be arranged symmetrically about thecentre of the furnace.

The rabble shafts 32 are driven by approved gearing as 39f from below orabove fluid (such as air or water), they the furnace, as preferred, andthe material to be treated is delivered into the top and discharged fromthe bottom of the furnace in any approved way. y x I The arms 33 on therabble shafts are so arranged that they move in more or less overlappingpaths and have teeth 34 (see Flg. 3) attached thereto which serve tostir the ore and to move it over the hearths. I

The rabble shafts 32 may be lagged as shown in Figure 3 with suitablerefractory material and provided with tilting arms 33 which are lockedin the shaft by their own weight. The shaft and arms employed in thefurnace are more less identical with those used in long hearth orstraight line furnaces and are small in size as'compared with thoseordinarily provided with superimposed circular hearth furnaces of equaldiameter.

If for any reasons it may be considered desirable to use arms cooled bya circulating any well known form.

The cusps 35 of the hearths which lie which the gases and ore pass fromone roastinc; chamber to another. The arrangementof the ports 36 asabove described provides that whilst the necessary area for the passageof the gases is furnished the number and area of the ports by which theore passes from hearth to hearth may be varied as required. withoutreducing the working area of the hearths.

Furthermore the arrangement of the ports for the passage of the orewithin the said cusps? enables the said ports to be disposed mainlyoutside the orbits ofthe rabbles. When the ports are located within theorbits of the rabbles an uneven distribution of ore on the hearth isoccasioned due to the thinning of the bed of ore by the dischargethrough the said ports. The arrangement of the ports in accordance withthis invention ensures an even bed of ore, increasesthe roastingcapacity of the furnace and prevents the formation of accretions 'orhard cakes of ore on the hearths.

In the furnace illustrated in Figures 1 to G of the drawings four rabbleshafts are shown passing 'ertically through all. the hearths and theserabble shafts are driven from beneath the furnace by gearing 32- from adriving shaft 38. V

The top 31' of thefurnace can be used as I a drying hearth for thematerial to be treated which passed by rahbling mechanism or rates (notshown) on the rabble shafts across the drier hearth to feed inlets 39 atthe sides thereof. The ore delivered to the top hearth 31 (whether fromthe drying hearth or from a superposed hopper) is may be of I blingmechanism operating over the second hearth moves the ore outwardly tothe ports 36 down which it falls on to the outer part of the thirdhearth and so on over all'the hearths of the furnace, or alternativelythe ore may be fed to the centre of the top hearth and hemoved'outwardly thereover and inwards on the next hearth and so onthrough the furnace. I 1

It will be obvious to one skilled in the art that the above mentionedmethod of rabbling will effectually stir the ore in the furnace andexpose it to'the furnace gases'and at the same time move itprogressively through the furnace. The ore is discharged through out letports 41 in the bottom hearth into trucks or other means for receivingand conveying it away from the furnace in any well'known way. I

The gases ascend and pass through the centre ports 40 in inwardlyrabbled'hearths. and through the ports 36 in outward rabbled hearths inopposite direction. to'themoveencroach on the rabbled portions of thecover hearth thereby enabling the said cover hearth to beused fordryingthe feed. A further advantage incidental to locating the offtake pipe 42in the position above described is. that its intake end is of compactform which would not otherwise be possible if the ofi'take led from thenarrow space left between the ore and the archabove around the peripheryof the top hearth 31'. I a

The arms preferably project alternately from opposite'sides 'of theshafts in their or'derupwards and all the shafts can be ar-' ranged torotate in the same direction or some of the shaftscan be rotated in onedi: rection and the other shafts in the reverse direction. i y Theplurality of symmetrically arranged rabbles' move the ore through thefurnace so as to allow it to receive variations intrca 1 ment asrequired. All the operations in the furnace are conductedwithoutinterruption so that whilst the productsof the reaction passcontinuously through the furnace the conditions of each stage of thetreatment in the furnace remain constant and continuity of operation anduniformity of product is ensured. I a

The sides of the furnace directly opposite the rabble shafts areprovided with openings 43 through which the arms 33 are introduced intothe furnace for attachment to the rain ble shafts; These openings 43permit of accessibility to the'iuterior of each of the roasting chambersfor effecting repairs and -=for other purposes and theyare normally way.

A fire-box ,or fire-boxes may be provided for supplying heat from anoutside source when required'but asfire-boxes of diiferent designs arecommonly used. with circular furnaces and form no part of this inventiontheyhave been omitted from the drawings though it s to be understoodthat I do. not

for convenience of illustration.

In lieu of arranging the ports 36 together with acentralport IO as abovedescribed so as'to passthe ore inwardly to and outwardly from the centreof siiccessive hearths the central port'tO can be dispensed with andthe-ports36 can be arranged so that the ore and gas will be passeddiametrically over :all the hearths.

This arrangement of thecirculation of the ore and gas is illustrateddiagrammatically in Figures 7, 8 and 9 which viewsare intendedtorepresent horizontal sections of a four shaft circular furnace takenover sucthesaid ports are. arranged on the opposite side of the furnace.When the ore and ports are arranged as above described the rabbles passthe ore diametrically across the hearths and in a zig-zag; mannerthrough the.

furnaceand the gases pass in-a reverse direction.

The ports 36 or drop holes'are. so arranged that the ore passesdown onlysuchports as will insure that, considering the direction of movement ofthe rabbles, there will be no likelihood of any considerable proportionof the i OPP/T8111?!lDlD tOO short a time on a hearth before passing tothe next hearth beneath.

separategas flues 37 are arepreferably located inside the cusps wellaway from the rabble orbits'and they 02111:.beextended upwardly beyondthe nor-' mal level of the ore. The object in locating' the upper endsof the gas fiues 37 above the level of the ore is to positively preventany ore entering and descending the same which would interfere with thenormal path of the ore through the furnace. I

Wliei1 the gas lines 37 are located entirely outside the orbits ofthe/rabbles 33 verylittle ofjthe ore will pass down the said gas flueseven when they do not extend above the normal level of the ore.

It will be obvious that the novel arrange ment of a plurality of shaftsin a circular furnace having superimposed heart-11s will suggest anumber of modifications-to one skilled in the art. In the diagrammaticviews illustrated in Figures 10 to 18 I have shown a number of such.modifications confine myself thereto. I a

In these diagrammatic views the path of the ore is indicated by thickarrows and the path taken by the gases is indicated by faint arrows.-

Figures 10 and 11 of the drawings are diagrammatic views representingsectional views of furnaces provided respectively with three and livesymmetrically arranged shafts, which rabble the ore in azig-zag manner.i

In Figure 12- is-shown a furnace provided with six rabble shafts thealternate shafts 45 being of smaller diameter and fitted with shorterarms than the other shafts 32.

In this view the gas and ore ports 36 are arranged so thatthe ore andgas will be passed diametrally overthe hearths but it will be obviousthat the ports canv he ar outside of alternate hearths and from theoutside to the centre of the intermediate hearths. I v

In Figures 13 and 14iis shown another arrangement of sixouter rabbleshafts surrounding a central rabble shaft 32 and the orbits'iof the armson the said outer shafts are adapted to overlap each other and alsooverlap the orbits ofthearins 33 on the central shaft. The ore and gasports in the hearths are disposed so asto cause the ore and gas to bemoved radially thereover from the centre to the outside ofthe furnace onalternate hearthsand vice-versa on intermediate heart'hs.

In Figures 15 and 16 is shown a different i each rabble shaft on theintermediate hearths.

In this method of passing the gas and ore through the furnace gas andore ports 46 are arranged around the shafts on each alternate hearth andin. the other hearths ports 36 and 47 are arranged respectively in thecusps and atthe centre of the said hearths.

The amount of ore transferred from the area commanded by one rabble tothe areas commanded by the adjacent rabblcs and vice-versa willapproximately balance anl this intermixing of the ore will ensure evenconditions on each hearth and a homogeneous furnace product.

In Figures 15 and 16 four rabble shafts 32 are shown but it will-beobvious that three or a greater number than four can be used and theports would then be located around all the shafts in each alternatehearth.

In the foregoing specification I have described different arrangementsof the gas and ore ports in the ihearths of the .rfurnace whereby theore will be passed across the hearths radially or diametrically or in aclirection radial to each of the rabble shafts.

It will, however, be obvious that one furnace can be constructed withports so arranged in the hearths that any one of the above-mentionedalternative methods of gas and ore movement may be used and a changefrom one to another can be readily effected.

The above 'menti-oned construction consists in arranging ports aroundthe periphery and at the centre of alternate hearths and at the centreand around the rabble shafts in the intermediate hearths. Those portsnot necessary for the method of rabbling required at the moment aretemporarily closed by suitable means and only those ports pertaining tothe desired move ment of the gas and ore left open.

Those portions of the cusps 35 not oc cupied by gas or ore ports may incertain instances be utilized for the accommodation of fines (not shown)for the vertical transference of gases and (or) air.

In a practical application of the invention the number and arrangementof the rabble shafts will depend upon the size of the furnace and alsoupon whether the central part of the furnace is to be used for accomwmodating a central stationary column 49.

WVhere a central stationary column 49 is not-required the preferredembodiment-of this invention comprises a furnace having four rabbleshafts 32 and where a central stationary column is required thepreferred embodiment comprises a furnace having six rabbles. In someinstances, however, as few as three rabble shafts can be usedefficiently and more than six rabble shafts may be used with or withouta central stationary column.

IV hen a number of rabbleshafts 32 (pref-- erably not less than six) areused with a central stationary column 49 they, are arrangedsymnietrically around the said, column shown in Figures 17 and 18 of thedrawings. I

This column 49 can be open to the air and means (such as sleeve valves50 arranged to slide therein) may be employed to control ports 51leading into the roasting chambers. The sleeve valves 50 are operated toopen or close the ports 51 by means of flexible members 52 which areconnected to rods 53 on the said valves and. pass over suitably disposedguide pulleys 54. In some instances the column 49 may be constructed sothat air (or any other gas) may be forced into it through the ports 51by a fan or other suitable means. v One or more sleeve valves 50 andports 51 can be provided (two being shown in the drawings) at that pointor those. points where it is desired to admit airto the roastinchambers. I g

I In Figures 19 and 20 this invention is shown as adapted for a mufflefurnace a .plu-. rality of shallow muffles 55v being detachably fittedto the central stationarycolumn 49. The muffles are shown applied to asix shaft furnace and are located in the second and third roastingchambers, and close to the underside of the first and second hearths 31so that the. rotating rabblearms will clear them. I r y I The mufllesare made of metal in the form of hollow arms and their inner ends aretapered to fit neatly into correspondingly tapered holes formed in thesides of the col-v umn 49. A close fitting joint may be effected betweenthe muffles and the column by means of screws or bolts 56 which passthrough the walls of the furnace and are supported by removable bracketsor bars 57 on the outside thereof or by other suitable means.

A central pipe 58 passes down thestationary columns anddistributingpipes 59 conduct the air therefrom to near'the outer ends of the muifles55 whence it returns to the central column 49. p

The cool air flowing through the muffles effectually cools the same andextracts arequired amount of heat from the roasting chambers. The heatedair from the mufiies passes down the column 49 and is delivered into thelower part ,ofthe furnace through ports in the side of the said columnor through hollow arms 62 detachably fitted thereto.

The hollow arms 62 are connected tosthe column and are supported attheir outer ends in the same way as the mufiies and the heated airdelivered thereto passes out open in'gs 63 nearthe outer ends thereof.If the lowermost hearth is inwardly rabbled. the arms (32 may bedispensed with and the heated air discharged from the column directlyintothe lowermost hearth.

The muiiles preferably are disposed over those parts of the hearthswhere a double rabbling of the ore is effected as the reaction is moreactive there and the rabble arm's being' at a maximum distance fr'omthearch at those points.

lVhen cooling only is required the metal muflles 55 may have their outerends open to the atmosphere through the walls of the furnace and theirinner ends open to the column 49 from which the heated air is withdrawnas required by a fan or by natural draught. I

Then the mullies are made as above described they can be readilyassembled and removed or replaced in sections by operating' through theports elet in the sides of the furnace. v

In; lieu of using metal muflles in conjunction with a central column 49as above described the he-arths of the furnace can have mutfles thereinin which case the top cover 6e of the muffle 65 (see Figures 21 and 22)is preferably made thicker than the lower cover 66 which consists of afalse arch suspended or built below the main arch. The stationary column49 in this case passes vert-ically through the centre of the hearths andis provided with a longitudinal partition 67 which divides the interiorinto two compartments 68 and 69.

Ports 70 are formed in the column on both sides of and near one edge ofthe partition 67 and these ports are arranged in line with passages 71'and 72 formed by three vertical partitions 73 arranged radially in then'iufiles.

The inner ends of the radial partitions 73 abut against the periphery ofthe central column and the outerv ends of the two outside partitions donot extend to the outer wall of the muflles.

When air is admitted to or forced into the compartment 68 it flowstherefrom through the passage 71 into the muflles from which it passesby way of the passage 72 and compartment 69to the outside'of the furnaceor to one or other of the roasting chambers as desired;

The mutHes 65 are preferably of less dilower end or suspended from itsupper end in any approved way. i

The transference of air from one point to another or the introduction ofair to the roasting chambers through the centre of the furnace is onlypossible with circular furnaces having rabbling mechanism construct edand arranged as hereinbefore described.

I claim:

1. A roasting furnace of circular or approximately circular shape havingsuperinr posed hearths separate provided with a plurality of verticalrabble shafts disposed symmetrically about the centre of the saidhearths and fitted with rabbles of a length substantially less than theradius of the said hearths and adapted to move in overlapping pathsabove each hearth whereby the ma terial on the hearths will beeffectually rabbled and moved progressively from hearth to hearththrough the furnace.

2. A roasting furnace of circular or approximately circular shape havingsuperimposed hearths provided with three or more vertical rabble shaftsdisposed symmetrically about the centre thereof and fitted with rabblesadapted to move in over lapping paths above each hearth and of a lengthsubstantially less than the radius of the said hearths, and ports in thehearths for gas andv ore so arranged that the ore will be moved in aradialdirection over each hearth and in a zig-zag manner progressivelythrough the furnace' V A roasting furnace of circular or ap proximatelycircular shape having su'perimposed hearths provided with three or morevertical rabble shafts disposed symmetrically about the centre thereofand fitted with rabbles adapted to move in overlapping paths above eachhearth and of a length substantially less than the radius of the saidhearth and ports in the hearths for gas and ore, arranged so that theore and will be moved diametrally, and in opposite directions overconsecutive hearths and progressively through the'furnace. i

a. rrroasting furnace of circular or approximately circular shape havingsuperimposed hearths provided with three or more vertical rabble shaftsdisposed symmetrically about the cen't-re thereof and fitted withrabbles adapted to move in overlapping paths above each hearth and of alength substantially less than the radius of the said hearth, and portsin the hearths for gas and ore so arranged that the ore will be movedradially towards each shaft within the orbits of each of the rabbles onalternateliearths and away from the shafts within the orbits of each ofthe rabbles on intermediate hearths.

5. A circular or approximately circular furnace having a series ofsuperimposed roasting chambers, a plurality of rabble i l l of thehearths, cusps on each hearth out side the orbits of the rabbles, gasand ore ports located within the said cusps on alternate hearths, andcombined gas and ore ports in the centre of the intermediate hearths.

6. A circular furnace having superimposed hearths provided withaplurality of vertical shafts disposed symmetrically about the centre ofthe hearths, said rabble shafts being fitted with rabblesof a lengthsubstantially less than the radius of the hearths V and adapted to movein overlapping paths, cusp shaped spaces on each hearth outside theorbits of the rabbles, ports for gas and ore having their major portionslocated within the said cusp shaped spaces on one side of alternatehearths, ports for gas and ore having their major portions locatedWithin the cusp shaped spaces on the opposite sides of the intermediatehearths and separate gas fines Within the same cusps as the gas and oreports.

7. A circular or approximately circular furnace having superimposedhearths provided with a plurality of shafts passing vertically throughand disposed symmetrically about the centre of all the hearths, shortrabbles on the shafts of a length sub stantially less than the radius ofthe hearths and adapted to move in overlapping paths, ports for ore andgas in the cusps around the outside and also in the centre of eachalternate hearth, and ports for ore and in the intermediate hearthssurrounding the shafts.

8. In a roasting furnace of circular or approximately circular shapeprovided with superimposed hearths, a rabble shaft passing centrallythrough the furnace, a plurality of rabble shafts passing verticallythrough the furnace and disposed symmetrically about "the centre shaft,and rabbles fitted to all the shafts of a length-substantially less thanthe radius of the hearths and adapted to move in overlapping paths.

9. In a roasting furnace of circular or approximately circular shapeprovided with superimposed hearths, a rabble shaft passing centrallythrough the furnace, a plurality of shafts disposed symmetrically aboutthe centre shaft, rabbles fitted to all the shafts of a lengthsubstantially less than the radius of the hearths and adapted to move inoverlapping paths, cuspson each hearth, ports for gas and ore havingtheir major portions located Within the cusps on alternate hearths, andports for ore and gas in the centre of the intermediate hearths andsurrounding the central rabbleshaft.

10. In a circular or approximately circular furnace as claimed-in claim1, a plu ra'lity of cusps on" the 'hearths near the wallof the furnaceand independent gas and ore ports arranged within or having their majorportion located within the cusps of the hcarths. I I 11. In a circularorapproximately circular furnace as claimed in claim 1, a plurality ofcusps on the hearths near the wall of th furnace and combined gas andore ports arranged within "the cusps on the hearths, j I

12, A circular or approximately circular furnacehaving "a"-seri.e,s ofsuper mposed heartlis and a plurality of rabble shafts passingvertically through the furnace and arranged symmetrically about thecentre thereof, rabble arms fitted to alternate rabble shafts of alength substantially less than theradius of the roasting chambers andarms of a shorter length on the intermediate rabble shafts.

13. In a circular or approximately circular furnace'as claimed in claim1, a sta tionary air circulating column independent of the rabbling'mechanism disposed vertically in the center of the furnace, and rabblearms on the symmetrically arranged rabble shafts adapted to clear thesaid column.

14. In a circular or approximately circu lar furnace claimed in claim 1,a ver tical column disposed centrally in the furnace', means forsupplying air or other gas to the column, ports in the side of thecolumn, arranged in communication with one or more of the roastingchambers and means for controlling the flow of air through the saidports. i

15. In a circular or approximately circular furnace as claimed in claim1, an air circulating column disposed centrally within. the furnace, andmufi'les in one or more roasting chambers arranged in communication withthe said central column,

16. In a circular or approximately circu- 1 lar furnace as claimed inclaim 1, means located w thin the furnace for preheating roasting airand means for delivering the preheated air to one or more of the lowerroasting chambers whereby control'of the temperature of the roastingchambers is effected.

17. In a circular or approximately. circular furnace as claimed in.claim 1, a column passing vertically through the centre of the furnace,mufiles extending radially from the central column and arranged incommunication therewith, means for passing cool air from the centralcolumn through the mufi'les and back to the said column and means forpassing the air heated by the mufHes to another part of the furnace.

18. In a circular or approximately circular furnace as claimed in claim1, a column supported centrally Within the furnace, muffle arms fitteddetachahly to the column and extending radially therefrom, means forsupporting the multle arms adjacent the crown of the roasting chambers,an air supply pipe Within the column having distributing pipesprojecting; into the muflle arms and outlets for the heated air from thelower part of the central column Wherehy the air returned to the centralcolumn through the mutl'le arms Wlll be directed into one of thelowermost roasting chambers.

19. In a circular or approximately circular furnace as claimed in claim1, a column supported centrally Within the furnace, a

partition disposed longitudinally within the column, ports in the columnon opposite sides of the partition therein, a mu'lile in one or morehearthsot the roasting chambers, a radial partition in the mutll'ealigning with the partition in the column, and

ARTHUR VIUIOR LEGGO.

Witnesses WM. A. HAIK, JOHN M. VEBBER.

